The number of Romanians and Bulgarians working in Britain rose by 8% in the second quarter of this year, according to the Office for National Statistics, still well short of the influx some predicted after border controls were fully lifted in January.

There were estimates that hundreds of thousands of Romanians and Bulgarians would come to Britain once the last of the seven-year transitional controls were lifted on the new EU members on 1 January, but the number in the workforce initially fell by 3,000 in the first quarter of the year, to 122,000.

The number increased to 132,000 between April and June, according to the ONS figures published on Wednesday, and was also up 4% on the same period last year, but Atul Hatwal, director of Migration Matters Trust, said the rise was nowhere near the scale predicted by Ukip.

"These figures expose the scale of scaremongering by Nigel Farage and Ukip over Romanian and Bulgarian migration," he said. "Farage predicted there would be 5,000 a week arriving for several years. Today's government statistics show that in the first six months the total rise in the numbers of Romanian and Bulgarian nationals was just 7,000.

"By the end of June, according to Ukip's forecast on Romanian and Bulgarian migration, the number should have been 130,000 – an overestimate of almost 20 times."

He added that the ONS figures included people coming to Britain for short periods of work, lasting a few weeks or months, whereas only those who came for 12 months or more counted towards the government's official net migration target. Hatwal said Farage "owes the country an apology for his reckless scaremongering last year".

Andrew Green, chairman of Migration Watch UK, claimed that the figures were in line with its predictions. "Once dependants are factored in it is likely that the increase in population over the whole year 2014 will be between 30,000 and 70,000 as we predicted," he said. "Our central estimate of 50,000 remains a very likely outcome."

The labour force figures show British workers took 73% of new jobs in the UK economy over the past year. UK nationals took 601,000 of the 820,000 extra jobs that had been created, compared with the 219,000 that went to foreign nationals. Foreign nationals now account for 2.89 million – 9.5% – of the UK workforce of 30.53 million.

The ONS also published figures for the UK workforce broken down by country of birth rather than nationality. By this measure the number of Romanians and Bulgarians rose by 13,000 in the second quarter of the year compared to the previous three months and by 12,000 compared to the same period last year.